Loosely bound DNA on mica

DNA Dynamics

These two movies (at 0.6 and 1.2 frames per second) show the dynamics of loosely bound DNA in liquid (Z range, 2 nm). The sample preparation used a lower than normal concentration of the divalent cations (Nickel in this case) that bind the DNA to the negatively charged mica. The reduced number of binding points allow long sections of the DNA to move freely.

In this case, the movie also gives insight into a common phenomenon seen when imaging DNA. In a single image, a DNA can appear to get cut, but then “repair” itself a frame later. The movie makes it clear that what actually happens is that a mobile section of the DNA can move while the tip is elsewhere on the scan line, so that it has “disappeared” when the tip reaches it. While several such “breaks” are obvious in the movie, from the motion of the strand, it is clear that the DNA remains undamaged and the “breaks” are a consequence of taking snapshots of a dynamic process.